Novel broccoli 1-aminocyclopropane-1-carboxylate oxidase gene (Bo-ACO3) associated with the late stage of postharvest floret senescence

Movement of ACC oxidase 3 mRNA from seeds to flesh promotes fruit ripening in apple

Xenia, the phenomenon in which the pollen genotype directly affects the phenotypic characteristics of maternal tissues (i.e., fruit ripening), has applications in crop production and breeding. However, the underlying molecular mechanism has yet to be elucidated. Here, we investigated whether mobile mRNAs from the pollen affect the ripening and quality-related characteristics of the fruit using cross-pollination between distinct Malus domestica (apple) cultivars. We demonstrated that hundreds of mobile mRNAs originating from the seeds are delivered to the fruit. We found that the movement of one of these mRNAs, ACC oxidase 3 (MdACO3), is coordinated with fruit ripening. Salicylic acid treatment, which can cause plasmodesmal closure, blocks MdACO3 movement, indicating that MdACO3 transcripts may move through the plasmodesmata. To assess the role of mobile MdACO3 transcripts in apple fruit, we created MdACO3-GFP-expressing apple seeds using MdACO3-GFP-overexpressing pollen for pollination and showed that MdACO3 transcripts in the transgenic seeds move to the flesh, where they promote fruit ripening. Furthermore, we demonstrated that MdACO3 can be transported from the seeds to fruit in the fleshy-fruited species tomato and strawberry. These results underscore the potential of mobile mRNAs from seeds to influence fruit characteristics, providing an explanation for the xenia phenomenon. Notably, our findings highlight the feasibility of leveraging diverse pollen genomic resources, without resorting to genome editing, to improve fruit quality.

Physiological and iTRAQ-based proteomic analyses reveal the function of exogenous γ-aminobutyric acid (GABA) in improving tea plant (Camellia sinensis L.) tolerance at cold temperature

BACKGROUND

Internal γ-Aminobutyric Acid (GABA) interacting with stress response substances may be involved in the regulation of differentially abundant proteins (DAPs) associated with optimum temperature and cold stress in tea plants (Camellia sinensis (L.) O. Kuntze).

RESULTS

Tea plants supplied with or without 5.0 mM GABA were subjected to optimum or cold temperatures in this study. The increased GABA level induced by exogenous GABA altered levels of stress response substances - such as glutamate, polyamines and anthocyanins - in association with improved cold tolerance. Isobaric tags for relative and absolute quantification (iTRAQ) - based DAPs were found for protein metabolism and nucleotide metabolism, energy, amino acid transport and metabolism other biological processes, inorganic ion transport and metabolism, lipid metabolism, carbohydrate transport and metabolism, biosynthesis of secondary metabolites, antioxidant and stress defense.

CONCLUSIONS

The iTRAQ analysis could explain the GABA-induced physiological effects associated with cold tolerance in tea plants. Analysis of functional protein-protein networks further showed that alteration of endogenous GABA and stress response substances induced interactions among photosynthesis, amino acid biosynthesis, and carbon and nitrogen metabolism, and the corresponding differences could contribute to improved cold tolerance of tea plants.

Exogenously induced expression of ethylene biosynthesis, ethylene perception, phospholipase D, and Rboh-oxidase genes in broccoli seedlings

In higher plants, copper ions, hydrogen peroxide, and cycloheximide have been recognized as very effective inducers of the transcriptional activity of genes encoding the enzymes of the ethylene biosynthesis pathway. In this report, the transcriptional patterns of genes encoding the 1-aminocyclopropane-1-carboxylate synthases (ACSs), 1-aminocyclopropane-1-carboxylate oxidases (ACOs), ETR1, ETR2, and ERS1 ethylene receptors, phospholipase D (PLD)-alpha1, -alpha2, -gamma1, and -delta, and respiratory burst oxidase homologue (Rboh)-NADPH oxidase-D and -F in response to these inducers in Brassica oleracea etiolated seedlings are shown. ACS1, ACO1, ETR2, PLD-gamma1, and RbohD represent genes whose expression was considerably affected by all of the inducers used. The investigations were performed on the seedlings with (i) ethylene insensitivity and (ii) a reduced level of the PLD-derived phosphatidic acid (PA). The general conclusion is that the expression of ACS1, -3, -4, -5, -7, and -11, ACO1, ETR1, ERS1, and ETR2, PLD-gamma 1, and RbohD and F genes is undoubtedly under the reciprocal cross-talk of the ethylene and PA(PLD) signalling routes; both signals affect it in concerted or opposite ways depending on the gene or the type of stimuli. The results of these studies on broccoli seedlings are in agreement with the hypothesis that PA may directly affect the ethylene signal transduction pathway via an inhibitory effect on CTR1 (constitutive triple response 1) activity.

Expression of 1-aminocyclopropane-1-carboxylate (ACC) oxidase genes during the development of vegetative tissues in white clover (Trifolium repens L.) is regulated by ontological cues

Four 5' flanking sequences, comprising the 5'-UTR and upstream promoter region, have been isolated and cloned from the 1-aminocyclopropane-1-carboxylate (ACC) oxidase gene family of white clover (Trifolium repens L.), and designated TR-ACO1p, TR-ACO2p, TR-ACO3p and TR-ACO4p. Southern analysis confirmed that these sequences correspond to four distinct genes. The four corresponding genomic sequences have also been isolated and each shown to be comprised of four exons interspersed by three introns. The expression pattern, in vivo, directed by all four 5' flanking sequences during leaf development has been examined using GUS fusions and transformation into white clover. Here, the TR-ACO1 5' flanking sequence directs highest expression in the apical tissues, axillary buds, and leaf petiolules in younger tissues and then declines in the ageing tissues, while the TR-ACO2 5' flanking sequence directs expression in both younger, mature green and in ontologically ageing tissue. The TR-ACO3 and TR-ACO4 5' flanking sequences direct more expression in the ontological older tissues, including the axillary buds and leaf petiolules. The TR-ACO1 5' flanking sequence directed expression in the ground meristem and newly emerged leaf tissue at the apical bud of the stolon, but all four 5' flanking sequences directed expression in the ground meristem tissue of axillary buds, vascular tissue, pith and cortex of the internode and node, and the cortex and vascular tissue of the leaf petiolule, with the primacy of each promoter determined by the ontological age of the tissues. These data suggest that in vegetative tissue development of white clover, the primary cues for the transcriptional regulation of the ACO gene family are ontological in nature.

Senescence-associated down-regulation of 1-aminocyclopropane-1-carboxylate (ACC) oxidase delays harvest-induced senescence in broccoli

To gain an in-depth understanding of the role of ethylene in post harvest senescence, we used broccoli (Brassica oleracea var. italica) as our model species. The senescence-associated asparagine synthetase (AS) promoter from asparagus was used to drive the expression of an antisense 1-aminocyclopropane-1-carboxylate oxidase (ACO) cDNA from broccoli, BoACO2, to reduce ethylene production following harvest. Physiological analyses revealed that transgenic broccoli lines harbouring the antisense BoACO2 gene construct (designated as AS-asACO) displayed delayed senescence in both detached leaves and detached heads as measured by hue angle. Harvested floret tissue from these plants also showed a delayed loss of chlorophyll, lower protease activity and higher total protein content, and changes in transcript levels of senescence marker genes when compared with wild type and transgenic lines transformed with an empty T-DNA. Genes that were down-regulated included those coding for cysteine protease (BoCP5), metallothionein-like protein (BoMT1), hexokinase (BoHK1), invertase (BoINV1) and sucrose transporters (BoSUC1 and BoSUC2). Northern analysis for BoACO1 and BoACO2, ACO assays and western analysis, revealed reduced ACO transcript, enzyme activity and protein accumulation, as well as reduced ethylene production in the transgenic AS-asACO lines when compared with controls, confirming that a key enzyme regulating ethylene biosynthesis was reduced in these plants. This, together with the changes observed in gene expression, confirm a significant role for ethylene in regulating the events leading to senescence in broccoli following harvest.